In order to prevent the loss of data on a main storage device when there is a power shutdown, a nonvolatile memory for saving data on a main memory may be installed in a storage controller. Patent Literature 1 discloses a technique for selecting only the main memory data that should be saved and saving the data to the nonvolatile memory. For example, it is supposed that the temporary storage destination for data pursuant to an access command from a higher-level apparatus is a volatile cache memory. When the supply of power from a primary power source to the volatile cache memory temporarily stops, the data being stored in the volatile cache memory is copied to a nonvolatile memory using power supplied from a battery.